1. Field of the Invention
The present invention relates generally to a communications system of a motor vehicle having a mobile phone with a first transceiver device for communicating on a first radio link between the mobile phone and a stationary transceiver system of a mobile radio system. The communication system preferably includes an audio and/or information system that is installed in the motor vehicle and has a receiver and an audio output unit and a microphone for implementation of a hands-free function. Voice and/or data transmission takes place between the mobile phone and the audio and/or information system over a wireless link. It is possible to output voice calls which are received at the mobile phone via the audio output unit.
2. Description of the Related Art
In order to operate mobile phones in motor vehicles safely when driving, hands-free devices are used which permit the driver to make a telephone call without having to hold the mobile phone. Such a hands-free device contains at least one microphone for picking up the voice of the driver or of another vehicle occupant and a loudspeaker for outputting the voice of the calling party. Appropriate hands-free devices can be mounted as stand-alone units in a vehicle and are connected to the mobile phone by means of an interface.
Because most motor vehicles have an audio system, as a rule a radio unit, solutions are known which also make use of the radio unit's loudspeakers for the hands-free device. In this case, a connection must be made between the radio unit and the mobile phone, and it is thus necessary to provide a mount for the mobile phone in the vehicle. The implementation of such a hands-free device is work-intensive, in particular when it is retrofitted in the motor vehicle, and requires cables to be laid.
WO 96/32783 discloses a hands-free device with which the installation effort can be reduced. For this purpose, an interface is provided which is connected to the mobile phone. The interface contains a transmitter unit for wireless transmission of the incoming voice signals of a telephone call to a radio unit in the vehicle. The signals that are transmitted by the interface are picked up by the radio unit's antenna and converted into audio signals in the radio receiver. These audio signals are fed to the loudspeakers via an amplifier. The transmission between the interface and the radio unit is carried out at any desired radio frequency in the AM or FM range. During an incoming call, the driver can thus listen to the incoming voice signals via the loudspeaker of the radio unit after he has selected the correct reception channel. The microphone is located in the interface mount. In this way, a hands-free device is implemented using a conventional radio unit which reduces the cabling complexity.
Nevertheless, in this hands-free device as well, the basic installation of the mount with the interface initially must be carried out in the motor vehicle. In addition, in each case the mobile phone has to be connected to the interface, with the result that every time the mobile phone is used in the motor vehicle certain handling steps are required.